Method of producing bunsen&#39;s salt



Patented Mar. 2, 1943 METHOD OF PRODUCING BUNSENS SALT Urner Liddel, Greenwich, and Robert B. Barnes, 'Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application July 10, 1940, Serial No. 344,700

8 Claims.

The present invention relates to a method of preparing Bunsens salt, to wit: tetra ammonium ferrocyanide, with two molecules of ammonium chloride of crystallization.

The usual method of the prior art is by reacdetrimental but a drop in temperature is definitely to be avoided. If the latter condition is disregarded, the product is contaminated with free ammonium chloride.

For example, a saturated solution of sodium tion between a solution of ferrocyanic acid or a ferrocyanide was made at about 45 C. Any salt thereof and a solution of ammonium chloother temperature below the decomposition point ride. Recovery of Bunsens salt from such a of the ferrocyanide is also suitable, although reaction mixture is diflicult, first, by reason of temper ur O 30 t0 C are preferred as the dilution thereof and second, because once 10 this range gives e s y S- 9 111018 o Solid in solution with ammonium chloride, it is diffiammon u C or e e t a d w y With cult to separate the two to obtain a product of stirring While pp y heal; t0 the reaction desired purity. mixture so as to maintain the temperature there- The principal object of the present invention, of at substantially 45 C. or slightly above. Buntherefore, is to prepare Bunsens salt in solid sens salt immediately is precipitated as pale form of good purity without the necessity of yellow crysta s which a be filtered from the extensive water removal and by a simple method. liquid and air dried. These crude crystals are It has been discovered that the above objects remarkably free from contaminating sodium may be accomplished if solid ammonium chloride Salts and e CeS ammonium r eis added to a saturated aqueous solution of an y erystallizing the Crude Salt from Water. 0011- alkali or alkaline earth metal (hereinafter retaminating impurities may be reduced to a minferred to as an alkali-forming metal) ferroi u cyanide, while maintaining the temperature of Bunsens salt finds extensive usefulness in the the reaction mixture no lower than that at which p t p art as it exhibits considerable the solution was originally saturated with the St b y in the presence of light- In the P ferrocyanide. Under these circumstances, Bunstate, however, it may be kept in subdued light sens salt precipitates immediately and almost for a Ils e e t o timequantitatively. The mixture should be filtered Whi e t e i ve tio h n de cr ed W t while at that temperature and without cooling particular reference to specific embodiments, it in order to avoid excessive contamination with is to be understood that it is not to be limited ammonium chloride. Recrystallization of the thereto but is to be construed broadly and rethus obtained crude Bunsens salt recovers the stricted solely by the scope of the appended latter in a state of exceptional purity and parclaims. ticularly free from undesirable quantities of am- We claim: monium chloride. 5 1. A method of preparing It is preferable to start with a saturatedsolu- (NH4)4Fe(CN)c-2NI-I 4Cl tion of sodium ferrocyanide. Ordinarily 8 mols which includes the steps of adding solid amof ammonium, chloride are required per mol of monium chloride to a saturated solution of an sodium ferrocyanide. However, under these ciralkali-forming metal ferrocyanide while maincumstances, the yield is low so that best results taining the temperature of the reaction magma are obtained when 9 or 10 mols of the former are no less than that at which the solution was used per mol of the latter. 9 mols gives optimum originally saturated with ferrocyanide. results. If more than 10 mols is added, the pre- 2. The method of claim 1 in which the ferrocipitate is badly contaminated with ammonium cyanide is of sodium. chloride which is most difiicult to remove. 3. The method of claim 1 in which from 8 It has been found important in producing solid to 10 mols of ammonium chloride per mol of Bunsens salt of good purity to maintain the temferrocyanide is added. perature at which the solution is saturated with 4. A method of preparing the alkali-forming metal ferrocyanide. When (NH4)4Fe(CN)s-2NH4Cl solid ammonium chloride is added thereto, its which includes the steps of adding 8 to 10 mols negative heat of solution has a tendency to lower of solid ammonium chloride to a saturated sothe temperature. Consequently, heat should be lution of sodium ferrocyanide and supplying supplied at a rate preferably no faster than heat heat to the reacting mixture at a rate sufficient is abstracted through ammonium chloride solu- I to counteract the negative heat of solution of tlon. A slight increase in temperature is not the ammonium chloride.

5. A method of preparing (NH4) 4Fe(CN) 6' 2NH4C1 which includes the steps of adding 8 to 10 mols of solid ammonium chloride to a solution-of sodium ferrocyanide saturated within the range of from 30 to 55 C. and supplying heat to the reacting mixture at a rate sufficient to counter act the negative heat of solution of the ammonium chloride.

6. A method of preparing (NH4)4Fe(CN)e NH4C1 1 which includes the steps of adding 9 mols of solid ammonium chloride to a solution of sodium ferrocyanide saturated at substantially 45 0., while supplying heat to prevent a temperature drop below 45 C.

7. The method of claim 6 with the additional steps of filtering the thus formed Bunsens salt andair drying the same.

8. The method of claim 6 with the additional step'of filtering the thus formed Bunsens salt, recrystallizing the same from water, and air 10 drying.

URNER LIDDEL. ROBERT B. BARNES. 

